=opacity( $pct )
  opacity: $pct/100
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=#{$pct})"
  filter: alpha(opacity='#{$pct}')

= user-select( $user_select )
  -moz-user-select: $user_select
  -khtml-user-select: $user_select
  -webkit-user-select: $user_select
  user-select: $user_select
  
// from http://gist.github.com/215561
// Apply a CSS text-shadow cross-browser.
// There is one todo/gotcha: the direction is hardcoded to towards 
// the bottom-right for IE, but that's good enough for my use case.
// Usage example: +text-shadow(#333, 1px, 1px, 1)

=text-shadow($color, $x, $y, $blur)
  text-shadow: $color $x $y "#{$blur}px"
  -ms-filter: "progid:DXImageTransform.Microsoft.Shadow(Color=#{$color},Direction=135,Strength=#{$blur})"
  
=background-size( $x, $y )
  -moz-background-size: $x $y
  -khtml-background-size: $x, $y
  -webkit-background-size: $x, $y
  -o-background-size: $x, $y
  background-size: $x, $y